The cool trick about stem cells is that they're super adaptable, and can become any other sort of cell, right? So why not use a mass of stem cells to regenerate a limb? Or grow an extra one? Well, it looks like it's all a bit more complicated than that. According to new research on the self-regenerating Zebrafish, the fish don't just form a mass of stem cells on a fin's stump to regrow the limb. Zebrafish actually use a slurry of cells, of different origins and with different purposes. Think salad, not soup.

Scientists figured this out by using a technique to make individual cells glow, which would be genetically passed down the lineage. They found that when they marked the cells from the skin of the stump, that glow was then found in the stem cells that formed on the wound, and then was passed on to the skin of the regenerated limb — but nowhere else. The same result was found with the nerves, pigment, blood vessels, bone and immune cells, for a total of nine different cell lineages required to play together nicely to put the limb back together.

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Sorry all you budding Wolverines. It's going to take more than just stem cells before you can become a regenerating, killing machine.